From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx143.netapp.com (mx143.netapp.com [216.240.21.24]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "mx143.netapp.com", Issuer "VeriSign Class 3 International Server CA - G3" (not verified)) by huchra.bufferbloat.net (Postfix) with ESMTPS id E6A9721F3F2; Fri, 15 May 2015 05:45:14 -0700 (PDT) X-IronPort-AV: E=Sophos;i="5.13,433,1427785200"; d="asc'?scan'208";a="42203489" Received: from hioexcmbx02-prd.hq.netapp.com ([10.122.105.35]) by mx143-out.netapp.com with ESMTP; 15 May 2015 05:44:11 -0700 Received: from HIOEXCMBX07-PRD.hq.netapp.com (10.122.105.40) by hioexcmbx02-prd.hq.netapp.com (10.122.105.35) with Microsoft SMTP Server (TLS) id 15.0.1076.9; Fri, 15 May 2015 05:44:11 -0700 Received: from HIOEXCMBX07-PRD.hq.netapp.com ([::1]) by hioexcmbx07-prd.hq.netapp.com ([fe80::f07f:691d:89d:53b7%21]) with mapi id 15.00.0995.031; Fri, 15 May 2015 05:44:11 -0700 From: "Eggert, Lars" To: "Bill Ver Steeg (versteb)" Thread-Topic: [Bloat] [Cerowrt-devel] heisenbug: dslreports 16 flow test vs cablemodems Thread-Index: AQHQjwItGDwMMmWczECnKhDrV0ZaOJ19cP6A Date: Fri, 15 May 2015 12:44:09 +0000 Message-ID: References: <8C015B1B-EFBA-4647-AD83-BAFDD16A4AF2@netapp.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.2100) x-originating-ip: [10.122.56.79] Content-Type: multipart/signed; boundary="Apple-Mail=_42E20A1A-F326-4B2D-9E3D-E7DC0816E2CA"; protocol="application/pgp-signature"; micalg=pgp-sha1 MIME-Version: 1.0 Cc: "cake@lists.bufferbloat.net" , "Klatsky, Carl" , "cerowrt-devel@lists.bufferbloat.net" , bloat Subject: Re: [Cerowrt-devel] [Bloat] heisenbug: dslreports 16 flow test vs cablemodems X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 May 2015 12:45:44 -0000 --Apple-Mail=_42E20A1A-F326-4B2D-9E3D-E7DC0816E2CA Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Hi, On 2015-5-15, at 13:27, Bill Ver Steeg (versteb) = wrote: > But the TCP timestamps are impacted by packet loss. You will sometimes = get an accurate RTT reading, and you will sometimes get multiples of the = RTT due to packet loss and retransmissions. right. But those will be transient, and so you can identify them against = the baseline. > You really need to use a packet oriented protocol (ICMP/UDP) to get a = true measure of RTT at the application layer. I disagree. You can use them to establish a lower bound on the delay an = application over TCP will see, but not get an accurate estimate of that = (because socket buffers are not included in the measurement.) And you = rely on the network to not prioritize ICMP/UDP but otherwise leave it in = the same queues. > If you can instrument TCP in the kernel to make instantaneous RTT = available to the application, that might work. I am not sure how you = would roll that out in a timely manner, though. That's already part of the TCP info struct, I think. At least in Linux. Lars > I think I actually wrote some code to do this on BSD many years ago, = and it gave pretty good results. I was building a terminal server = (remember those?) and needed to have ~50ms +- 20ms echo times. >=20 >=20 > Bvs >=20 > From: bloat-bounces@lists.bufferbloat.net = [mailto:bloat-bounces@lists.bufferbloat.net] On Behalf Of Eggert, Lars > Sent: Friday, May 15, 2015 4:18 AM > To: Aaron Wood > Cc: cake@lists.bufferbloat.net; Klatsky, Carl; = cerowrt-devel@lists.bufferbloat.net; bloat > Subject: Re: [Bloat] [Cerowrt-devel] heisenbug: dslreports 16 flow = test vs cablemodems >=20 > On 2015-5-15, at 06:44, Aaron Wood wrote: > ICMP prioritization over TCP? >=20 > Probably. >=20 > Ping in parallel to TCP is a hacky way to measure latencies; not only = because of prioritization, but also because you don't measure TCP = send/receive buffer latencies (and they can be large, auto-tuning is not = so great.) >=20 > You really need to embed timestamps in the TCP bytestream and echo = them back. See the recent netperf patch I sent. >=20 > Lars --Apple-Mail=_42E20A1A-F326-4B2D-9E3D-E7DC0816E2CA Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="signature.asc" Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- iEYEARECAAYFAlVV6hcACgkQIWcjmsUTWRoUOACeLz3jT09xkRjz7gfQ4nLvDFJb IjQAoN062KSgeZ/GSdAR2iBJJHP3+zZg =S7wR -----END PGP SIGNATURE----- --Apple-Mail=_42E20A1A-F326-4B2D-9E3D-E7DC0816E2CA--